In the past few decades, the petroleum industry has invested heavily in the development of marine seismic survey techniques that yield knowledge of subterranean formations beneath a body of water in order to find and extract valuable mineral resources, such as oil. High-resolution seismic images of a subterranean formation are essential for quantitative seismic interpretation and reservoir monitoring. For a typical marine seismic survey, an exploration-seismology vessel tows a seismic source, and the same vessel, or another vessel, tows one or more streamers that form a seismic data acquisition surface below the surface of the water and above a subterranean formation to be surveyed for mineral deposits. The vessel contains seismic acquisition equipment, such as navigation control, seismic source control, seismic receiver control, and recording equipment. The seismic source control causes the seismic source, which is typically an array of source elements, such as air guns or marine vibrators, to produce acoustic impulses at selected times. Each acoustic impulse is a sound wave that travels down through the water and into the subterranean formation. At each interface between different types of rock, a portion of the sound wave is transmitted and another portion is reflected back into the body of water to propagate toward the surface. The streamers towed behind the vessel are elongated cable-like structures. Each streamer may include a number of seismic receivers or multi-component sensors that detect pressure and/or particle motion wavefields associated with the sound waves reflected back into the water from the subterranean formation.
Sound waves that propagate down into the subsurface and undergo a single reflection from an interface before being detected by seismic receivers are called “primary reflections,” and sound waves that are reflected within the subterranean formation and/or reflected from the free surface before being detected by seismic receivers are called “multiple reflections.” In the past, conventional imaging techniques relied almost exclusively on the primary reflections. As a result, significant computational effort was dedicated to attenuating the multiple reflections. In recent years, however, the multiple reflections have been recognized as providing additional, valuable information about the subterranean formation. In particular, multiple reflections that include at least one reflection from the free surface, called “free surface multiples,” are typically the strongest and most significant of the multiple reflections to use in imaging a subterranean formation. Geophysicists, petroleum engineers, and others working in the petroleum industry continue to seek systems and methods that improve the quality of subterranean images.